Abstract: Voltage sag, as one of the greatest power quality problems, has been seriously threatening the operation of modern industry and public services. The fast and accurate detection of voltage transient events is an important part of transient drop management. Traditional sag detection algorithm based on single synchronous reference frame phase-locked loop and instantaneous d-q decomposition cannot give an accurate and fast detection on grid voltage containing negative sequence and harmonic components. We propose and study in detail the voltage spectrum shifting process based on the Park coordinate transformation of the estimated reference phase, and extract the effective components of the grid voltage with the help of discrete sliding average filtering, so as to realize the fast and accurate detection of voltage transients with negative sequence and harmonic components without phase locking loop. The proposed method is simple and adaptable, it can save chip computing power and avoid the detection delay caused by dynamic process of PLL during voltage sag, also realize a rapid extraction of harmonic components in specific order. Simulation and HIL experiments based on PLECS and RT Box have verified the effectiveness, quickness and simplicity of proposed algorithm. The reliability of proposed algorithm has been further verified by a 10 kV dual power fast switches device with the background of voltage sag prevention in an electronics industrial park in Guangdong, China.